Gas turbine engines such as those used as aircraft turbojets or turbofans typically comprise a rotating fan, a low-pressure compressor and a high-pressure compressor as well as high-pressure and low-pressure turbines that are axially mounted to separate coaxial shafts for rotation about a central axis of the engine. The high-pressure compressor typically includes a set of multiple axial stage rotors followed by a centrifugal impeller. Enshrouding the blades of the centrifugal impeller is a static impeller shroud. The impeller shroud is typically mounted to one of the engine cases in the compressor section such as, for example, by means of a strut that extends from the impeller shroud radially outwardly to the inner case of the bypass duct. The strut secures the impeller shroud in place relative to the impeller blades so that there is a minimal clearance between the impeller blades and the impeller shroud. Minimizing the clearance between the impeller blades and the impeller shroud is instrumental in optimizing the capacity of the impeller to pressurize the air to the elevated pressures required for high engine performance.
Due to thermal and other external loads, the impeller shroud may deflect. External loads include externally applied loads from the assembly fit as well transient operating conditions. Deflections of the impeller shroud are most pronounced at the tip of the shroud. Likewise, the deflections and distortions of the impeller blades due to thermal effects and centrifugal loading is most pronounced at the tips of the blades. Therefore, controlling variations in the tip clearance, i.e. the gap between the tip of the impeller blades and the impeller shroud as these two components move relative to each other, is critical to optimizing pressurization and thus engine performance. In other words, tip clearance should be tight enough to ensure strong pressurization of the air discharging from the impeller but it must not be so tight that there is a risk that deflections of the impeller shroud relative to the impeller (due to extreme thermal or other loads) can cause the blades and the shroud to come into contact with each other.
Accordingly, there is a need to provide an impeller shroud that is isolated from thermal loads and other external loads so as to maintain an unvaryingly tight tolerance on tip clearance.